The present invention relates to a novel and improved furnace process for easily and steadily producing carbon blacks having lower specific surface area and structure levels than it is possible to produce in a conventional furnace carbon black process. The carbon blacks produced by the process of the present invention are suitable for various applications including fillers, reinforcing agents and color pigments in rubbers and plastics.
In a conventional furnace process for producing carbon black, liquid hydrocarbon feedstock is pyrolyzed by a hot primary combustion gas stream generated from a mixture of fuel and oxidant, such as preheated air or the like, to form an effluent stream. Pyrolysis of the feedstock is stopped by a quench and carbon black products are separated and recovered from the quenched gas stream.
The specific surface area of carbon black produced by furnace process depends, generally, upon decomposition reaction temperature which is controlled by primary combustion gas temperature and the amount of feedstock introduced.
Generally, the specific surface area of carbon black decreases with falling reaction temperature, which decreases with falling primary combustion gas temperature and with an increase in the amount of feedstock introduced. However, temperature of the primary combustion gas cannot be decreased without any limitation, because the primary combustion gas supplies energy for decomposition of the feedstock. Therefore, production of carbon blacks having such a low specific area in furnace process is generally accomplished by increasing the amount of feedstock introduced which leads to a need to shut down the reactor for cleaning as a result of carbon black adhering to the inside of the reactor walls as indicated by low light transmittance of toluene discoloration.
Provided that the amount of feedstock introduced is increased, the amount of carbon black produced per unit volume of the reactor is increased and as a result, promoted coke formation leads to increased grit as an impurity which means deterioration of carbon black quality. In order to resolve this problem, the reaction zone may be expanded but expansion of the reaction zone may lead to a new problem of accumulation of carbon black formed due to slowdown of effluent gas speed in the reactor and also an undesirable economic problem associated with the need for enlarged facilities.
Primary particle diameter of the carbon black is generally dependent upon the reaction temperature. The higher the reaction temperature, the smaller is the primary particle diameter of the carbon black formed. The higher the structure of a carbon black, the lower is the specific area of the carbon black at a given particle size. This means that low structure blacks have higher specific surface area at a given primary particle size than high structure blacks.
Restriction of carbon black structure development is attained in conventional processes by introduction of alkali metals ion into the reactor, but this method generally causes an increase of specific surface area simultaneously with decreasing structure because the primary particle diameter remains generally constant. It will, therefore, be recognized that production of carbon blacks having both low structure and low specific surface area is difficult in heretofore conventional furnace processes.
For the purpose of solving this type of problem, U.S. Pat. No. 5,190,739 gives important suggestions of production method of carbon blacks having both low structure and low specific surface area at a given overall combustion level, which gives an important suggestion to a method for preparing carbon blacks having both low structure and low specific surface area at a given feedstock level introduced. This method is carried out by adding an auxiliary hydrocarbon such as an auxiliary hydrocarbon having high molar hydrogen-to-carbon ratio or hydrogen.
Technology relating to the introduction of water or steam into furnace carbon black reactors is disclosed in U.S. Pat. No. 4,283,378 and U.S. Pat. No. 4,631,180. Technology relating to introduction of water or steam as an improved method for producing carbon black based on furnace process, was also described in Japanese Patent Publication No. Sho54-7634, Japanese Patent Laid Open No. Sho56-24455, and Japanese Patent Laid Open No. Hei 3-128974 etc. All of these inventions generally relate, however, to production of carbon blacks having higher specific surface areas than the carbon blacks produced in a similar manner in the absence of steam activation. Thus, the objective of these inventions is quite different from that of the present invention relating to production of carbon blacks having lower specific surface areas than carbon blacks produced in a similar manner in the absence of steam activation.
Accordingly, an object of the present invention is to develop an improved furnace carbon black process in order to produce easily and steadily carbon blacks having both low specific surface area and low structure which have been regarded as being difficult to produce by conventional furnace process.
The above-mentioned object, and other advantages are attained by an improved furnace carbon black process featuring restraint both of specific surface area and structure developments by means of introduction of steam at or near the position of introduction of feedstock in furnace carbon black process. According to the process of the present invention, in a furnace carbon black production process comprising introduction of hydrocarbon feedstock, preferably in liquid form, into hot primary combustion gas stream, pyrolysis and quenching, steam is introduced into the combustion gas stream at, or near (upstream or downstream), the point of the injection of the hydrocarbon feedstock into the gas stream such that the ratio L/D (as hereinafter defined) ranges from 0 to less than 1.0.